The human heart has four cardiac valves: the mitral valve, the tricuspid valve, the pulmonary valve and the aortic valve. The mitral valve is situated in the left atrioventricular ostium and ensures that the blood flows in one direction from the atrium to the ventricle. It opens in the diastoles and closes in the systoles, preventing the blood from flowing back from the ventricle to the atrium. The shape, dimensions and flexibility of the annulus of a normally functioning mitral valve are such as to enable the valve lips to close correctly during the systolic phase. The mitral annulus has, for instance, a characteristic “kidney” (or “D”) shape and is more flexible in the portion corresponding to the posterior lip of the valve. Diseases and genetic defects may cause the annulus of the mitral valve to be deformed or dilated with the result that it does not close completely and there is therefore a regurgitation of blood. This problem may also occur in the tricuspid valve situated between the right atrium and the right ventricle.
A method frequently used to eliminate some pathological impairments of the mitral and tricuspid valves is to return the valve annulus to its correct shape and dimensions by surgical procedures known as annuloplasty.
Annuloplasty consists in the surgical implantation of a support prosthesis on the dilated or deformed annulus, in order to return it to its physiological shape and/or dimensions so that the cardiac valve can function correctly. The support prostheses used in valve repair surgery are known as annuloplasty prostheses. In most cases, these prostheses are formed by a closed or open ring structure comprising an inner ring-shaped member and an outer coating of biocompatible material which enables its surgical suturing.
Various kinds of annuloplasty prostheses have been disclosed in the prior art. Prostheses whose rigidity may be made variable in a desired manner depending on the point, the direction and/or the method of application of stresses are in particular already known. For instance, U.S. Publication 2003/0220686 discloses various embodiments of an annuloplasty prosthesis comprising an inner tubular member having a plurality of apertures in at least one portion of its wall.